1. The Field of the Invention
The present invention relates to drill heads and to drill heads configured to generate oscillating vibratory forces.
2. The Relevant Technology
Core drilling allows samples of subterranean materials from various depths to be obtained for many purposes. For example, drilling a core sample and testing the retrieved core helps determine what materials are present or are likely to be present in a given formation. For instance, a retrieved core sample can indicate the presence of petroleum, precious metals, and other desirable materials. In some cases, core samples can be used to determine the geological timeline of materials and events. Accordingly, core samples can be used to determine the desirability of further exploration in a given area.
Although there are several ways to collect core samples, core barrel systems are often used for core sample retrieval. Core barrel systems include an outer tube with a coring drill bit secured to one end. The opposite end of the outer tube is often attached to a drill string that extends vertically to a drill head that is often located above the surface of the earth. The core barrel systems also often include an inner tube located within the outer tube. As the drill bit cuts formations in the earth, the inner tube can be filled with a core sample. Once a desired amount of a core sample has been cut, the inner tube and core sample can be brought up through the drill string and retrieved at the surface.
Sonic head assemblies are often used to vibrate a drill string and the attached coring barrel and drill bit at high frequency to allow the drill bit and core barrel to slice through the formation as the drill bit rotates. Accordingly, some drilling systems include a drill head assembly that includes both a sonic head assembly to provide the high frequency input and a rotary head to rotate the drill string. The sonic head includes eccentrically weighted rotors that are oscillated. The eccentrically weighted rotors are coupled to a shaft. The shaft can in turn be coupled to a drill rod such that turning the eccentrically weighted rotors transmits a vibratory force from the shaft to the drill rod.
In order to allow the rotation described above, a number of bearing configurations are often provided to support the shaft as it rotates. The life of the bearings depends, at least in part, on maintaining an appropriate pre-load to maintain contact between the bearings and the shaft. In the past, bearings have often been located in positions that required disassembly of the head in order to adjust the preload on the bearings. Adjusting the pre-load could also be tedious. If the pre-load was not maintained, the vibratory forces generated by rotation of the eccentrically weighted rotors would quickly destroy the bearings or other parts of the drill. These repairs would often result in substantial down-time as operators repaired or replaced the bearings or other components of the sonic head assembly.
The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one exemplary technology area where some embodiments described herein may be practiced.